Refining mineral oils



Feb. 17, 1942.` W, o, QILMAN v2,273,104

REFINING MINERAL OILS Filed Feb. 24, 1941 ALKAL l .SoLuTlo/V spew 'r AL KA 1.1 j .//l au. rre a PkoDucT CON THQT/NG 2 GIVE .sPEN-r au 1./ l

l /4 l5 ALkAL/ sronAce TANK Patented Feb. 17, 1942 REFDNG MINERAL GILS William 0. Heilman, Cranford, N. J., assignor to Standard Oil Development Company, a corporation of Delaware Application February 24, 1941, Serial No. 380,272

(Cl. 19d-32) l Claims.

The present invention is concerned with the refining of mineral oils. This invention is more particularly concerned with the removal oi mercaptan compounds from petroleum oils, particularly from petroleum oils boiling in the heavy naphtha heating oil and gas oil boiling ranges. In accordance with the present process, objectionable mercaptan compounds are removed from oils of this character by a process in which the feed oil is segregated into a relatively high and into a relatively low boiling range fraction. The relatively low boiling range fraction is contacted with an alkali metal hydroxide solution under conditions to secure substantial complete re'- moval of the mercaptan compounds therefrom. This is secured by utilizing a relatively large amount of alkali metal hydroxide solution as compared to the volume of relatively low boiling feed oil being treated. The partially spent alkali metal hydroxide solution is then utilized for the removal of the mercaptan compounds from the relatively high boiling range fraction.

It is known in the art to renne petroleum oils by various operations in order to produce products of a satisfactory quality. For example, it is known in the art to remove objectionable mercaptan compounds by various operations. One operation comprises treating the mercaptancontaining feed oil with a so-called doctor solution which comprises a sodium hydroxide solution of lead oxide under conditions to convert the mercaptan compounds to disulfide compounds. This operation does not reduce the total sulfur content of the oil but merely converts the sulfur compounds into relatively innocuous materials. In an operation of this character, the process usually comprises treating the lead mercaptide bearing oil with free sulfur in a manner to precipitate lead sulde and to form the corresponding alkyl disuldes. The disadvantage of an operation of this character is that considerable care must be exercised with respect to the addition ofY the free sulfur. If insuicient sulfur is added all the mercaptides are not removed from the oil, which results in a product of inferior quality. On the other hand, if an excess of sulfur be added, this excess sulfur remains dissolved in the treated oil which increases its corrosiveness and in many instances necessitates rerunning of the oil, Thus, various suggestions have been made that objectionable compounds, such as mercaptans, be removed from the oil in a manner to completely free or at least considerably lower the totalrsulfurV content of the treated oil. For example, it has been suggested that the oils be treated with an alkali metal hydroxide solution such as with a sodium hydroxide solution. However, in order te remove the mercaptan compounds satisfactorily, particularly the relatively high boiling mercaptan compounds, it is necessary to use a relatively large quantity of the reagent based upon the volume of oil treated. This is particularly the case when treating relatively high boiling oils as, fer eX- ample, those oils boiling in the heavy naphtha, heating oil, and gasoil ranges, as for example, those oils which boil in the general range from 250 F. to about 750 F.

I have, however, now discovered a process by which a relatively low total quantity of alkali metal hydroxide solution may be used as compared to the total volume of feed oil being desulfurized. In accordance with my invention, the feed oil is segregated into a relatively low boiling fraction and into a relatively high boiling fraction. The relatively low boiling fraction is contacted with the total volume of alkali metal hydroxde solution whereby the ratio of alkali metal hydroxide solution to the quantity of oil being treated is relatively high, since only a relatively small amount, that is the low boiling fraction, is contacted. Under these conditions, when utilizing a relatively large amount of alkali metal hydroxide solution to feed oil, substantial co i-- plete removal of the mercaptan compounds is obtained. The partially spent alkali metal hydroxide solution containing the lower boiling mercaptans present as mercaptides, and likewise containing constituents which function to enhance the afnity of the partially spent alkali metal hydroxide solution for the relatively higher boiling mercaptans present in the higher boiling segregated fraction, is utilized in contacting the segregated relatively higher boiling feed fraction in a secondary treating zone. Under these conditions substantial complete removal of the mercaptan compounds is secured from both the relatively high and the relatively low boiling seggregated fraction of the feed oil.

My process may be readily understood by reference to the attached drawing illustrating an embodiment of the same. For purposes of description, it is assumed that the feed oil cornprises a heating oil fraction boiling the vgeneral range from about 250 F. to 6G00 F. The feed oil is introduced into a distillation zone l by means of line 2 in which it is segregated into a i relatively low boiling fraction which is removed by means of line 3 and a relatively high boiling fraction which is removed by means of line 4.

'Ihe relatively low boiling fraction is cont-acted in an initial treating zone 4 with an alkali metal hydroxide solution which for the purpose of description is taken to be a sodium hydroxide solution. The sodium hydroxide solution is Withdrawn from sodium hydroxide storage 6 and introduced into contacting zone 4 by means of line 5. Operating temperature and pressure conditions and the quantity of sodium solution used are adapted to secure substantially complete removal of the mercaptan compounds from the segregated relatively low boiling fraction of the feed oil. The treated segregated oil fraction, free of mercaptan compounds, is withdrawn from contacting zone 4 by means of line 'I While the spent sodium hydroxide solution is withdrawn by means of line 8 and passed into secondary contacting zone 9. In secondary contacting zone 9 the spent sodium hydroxide solution contacts the relatively high boiling segregated fraction of the feed oil under conditions to remove the relatively high boiling mercaptan compounds from this segregated fraction of the feed oil. The relatively high boiling segregated fraction of the feed oil free of mercaptan compounds is withdrawn from contacting zone 9 by means of line I and preferably combined with the segregated low boiling fraction of the feed oil removed from zone 4. The total feed oil is withdrawn from the system by means of line II, and further rened or handled in any manner desirable. The spent sodium hydroxide solution is withdrawn from contacting zone 9 by means of line I2 and passed to regeneration zone I3 in which the sulfur compounds are removed therefrom preferably by steam to convert the same to mercaptans which are removed overhead by means of line I4. Sludge and soap constituents are removed as a bottoms by means of line I while the regenerated sodium hydroxide solution is removed by means of line IIi and recycled to zone 4. Under certain conditions, it may be desirable to remove the mercaptide coinpounds from the partially spent sodium hydroxide solution removed by means of zone 4 before introducing the same into zone 9. If this adaptation of the invention be employed, the partially spent sodium hydroxide solution is introduced into zone I'I by means of line I8 in which the mercaptides are converted to mercaptans and removed overhead by means of line I9. The partially spent solution free of mercaptans is withdrawn from zone Il by means of line and passed to contacting zone 9 as described.

The process of the present invention may be widely varied. It is to be understood that zones I, 4, 9, I'I and I3 may comprise any suitable number and arrangement of units. The process essentially comprises utilizing a relatively large volume of alkali metal hydroxide solution on a segregated relatively low boiling fraction of a feed oil, removing the partially spent alkali metal treating reagent and utilizing the same for treating the relatively high boiling segregated fraction of the feed oil from which the mercaptans are more dicultly removable. By segregating the feed oil as described, the quantity of the treating reagent is at least doubled providing the feed oil be segregated into approximately equivalent volumes. Thus the effectiveness of the reagent in removing the mercaptans from the relatively low boiling segregated fracti-on is increased approximately 100%. I have found that the partially spent reagent after removal from the relatively low boiling fraction is more effective in the removal of the more diicultly removable mercaptans from the high boiling fraction than fresh reagent. Although I do not wish to be limited by any theory or mechanisms or with respect to the reactions involved, it appears that the alkali metal hydroxide solution absorbs constituents from the relatively 10W boiling segregated fraction of the feed oil which materially enhances its afnity, although partially spent, for the more diicultly removable mercaptans.

The invention may be adapted for the treatment of any relatively high boiling petroleum feed oil. It is, however, particularly suitable for use in treating petroleum oils boiling in the heavy naphtha, heating oil, land gas oil boiling ranges, as for example, for the treatment of petroleum oils boiling in the range from about 250 F. to about 700 F. It is particularly effective in the treatment of heating oils such as those boiling in the range from about 250 F. to 600 F. In general, it is preferred to segregate a feed oil into two fractions in which the final boiling point of the low boiling fraction and the initial boiling point of the high boiling fraction approximate the mid-boiling point of the feed oil. Thus, for example, when treating petroleum oils boiling in the range from about 250 F. to 600 F., it is preferred that the final boiling point of the relatively low boiling fraction be in the range from about 425 F. to 450 F., and the initial boiling point of the high boiling fraction be in the range from about 400 F. to 425 F. A particular adaptation of the present invention is in the treatment of a petroleum oil fraction boiling in the range from about 400 F. to 650 F. Under these conditions, the final boiling point of the relatively low boiling fraction is about 525 F. to 550 F., whereas the initial boiling point of the relatively high boiling fraction is in the range from about 500 F. to 525 F.

Although any alkali solution may be used, I particularly prefer to employ alkali metal hy- -droxide solutions, especially a sodium hydroxide solution. When utilizing a sodium hydroxide solution, I prefer to use a solution of from about 15 to 25% sodium hydroxide solution and to use from about 0.2 to 0.4 volume of sodium hydroxide solution per volume of oil.

The manner in which the feed oil is segregated may be varied widely. In general, the relatively low boiling fraction should not comprise over 50% of the total volume of oil and should preferably comprise less than this amount. A very desirable operation is to segregate a relatively low boiling fraction comprising from about 10% to 30%, preferably about 20%, of the oil as the low boiling fraction.

What I claim as new and wish to protect by Letters Patent is:

1. Process for the removal of mercaptan compounds from oils boiling above about 250 F., which comprises segregating the feed oil into a relatively low boiling fraction and into a relatively high boiling fraction, treating said relatively loW boiling fraction in a primary lcontacting zone with an alkali metal hydroxide solution under conditions to remove the mercaptan compounds therefrom, separating the relatively low boiling treated oil from the alkali metal hydroxide solution, removing the respective streams of said low boiling treated oil and said alkali metal solution from the primary contacting zone, treating the relatively high boiling fraction in a secondary contacting zone with the separated alkali aevaioi metal hydroxide solution removed from said primary zone under conditions to remove the mercaptan compounds therefrom, separating the relatively high boiling treated oil fraction and combining the same with the relatively low boiling treated oil fraction to produce a final nished product.

2. Process as dened by claim 1, in which the alkali metal hydroxide solution comprises a sodium hydroxide solution.

3. Process as defined by claim 1, in which the alkali metal hydroxide solution withdrawn from the primary contacting zone is treated in a manner to convert the cercaptides to mercaptans which are removed from the alkali metal hydroxide solution before utilizing the same in contacting the relatively high boiling fraction.

4. Process for the removal of mercaptan compounds from petroleum oils boiling above about 250 F., which comprises segregating the oil into a relatively low boiling fraction comprising from about 10% to 30% of the total feed oil and into a relatively high boiling fraction comprising from about 70% to 90% of the total feed oil, treating the relatively low boiling fraction in a primary contacting zone with an alkali metal hydroxide solution under conditions to remove therefrom the mercaptan compounds, separating the relatively low boiling treated oil fraction from the alkali metal hydroxide solution, utilizing said latter solution for contacting the relatively high boiling oil fraction in a secondary contacting zone under conditions to remove from the oil fraction mercaptan compounds, separating the relatively high boiling treated oil fraction and combining the same with the relatively 10W boiling treated oil fraction to produce a finished high quality product.

5. Process as defined by claim 4, in which the alkali metal hydroxide solution comprises a sodium hydroxide solution.

6. Process as dened by claim 4, in which the alkali metal hydroxide solution withdrawn from the primary contacting zone is treated in a manner to convert the mercaptides to mercaptans which are removed from the alkali metal hydroxide solution before utilizing the same in contacting the relatively high boiling fraction.

'7. Process as dened by claim 4, in which said oil boils in the range from about 400 F. to 700 F.

WILLIAM O. HEILMAN. 

